<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
  <style>
    #d1{
      width: 100px;
      height: 100px;
      border: 1px solid red;
/*      margin-left: 50px;
      margin-top: 50px;
      margin-bottom: 50px;*//*单独某一个方向赋值*/

      /*margin: 50px;!*四个方向赋值*!*/

      /*margin: 50px 100px;!*上下 和 左右赋值*!*/

      margin: 10px 20px 30px 40px;/*上右下左顺时针赋值*/
    }
    #d2{
      width: 100px;
      height: 100px;
      border: 1px solid blue;
        margin-top: 20px;/*上下相邻取最大值*/
    }
    #s1{
        border: 1px solid blue;
        margin-right: 50px;
        /*margin-top: 50px;!*行内元素上下边距无效*!*/
    }
    #s2{
        /*左右相邻彼此添加外边距相加*/
        margin-left: 30px;
    }

    #big{
        width: 200px;
        height: 200px;
        background-color: red;
        overflow: hidden;
    }
    #big>div{
        width: 50px;
        height: 50px;
        background-color: green;
        margin-left: 50px;
        /*当元素的上边缘和上级元素的上边缘重叠时
        给元素添加上外边距会出现粘连问题*/
        margin-top: 50px;
    }
    body{
        margin: 0;/*去掉自带外边距*/
    }
    p{margin: 0}
    ul{margin: 0}
    *{margin: 0}
  </style>
</head>
<body>
<ul>
    <li>aaa</li>
    <li>bbb</li>
</ul>
<h1>这是h1</h1>
<p>pppp</p>

<div id="big">
    <div></div>
</div>
<span id="s1">span1</span>
<span id="s2">span2</span>
<!--div#d1-->
<!--div.c1-->
<!--div*3-->
<div id="d1"></div>
<div id="d2"></div>
</body>
</html>